The one thing that stands out to me as lacking in the Next+Blitz vs Remix comparison is form handling. It's a real pain in the butt if you want to use Next with progressively-enhanced forms - even with helpers like next-runtime you have to roll a lot of the basics like validation and type coercion from form submits yourself.
It feels like it stands out even more because of mutation handlers, which on the Remix side are generally set up as "just" form posts that update after a success.